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R C Roberts

Publications and source records attributed to R C Roberts.

At least 19 recordsLinked to original sources
PubMed1992

Immunocytochemical localization of kynurenine aminotransferase in the rat striatum: a light and electron microscopic study.

Kynurenine aminotransferase is the biosynthetic enzyme for kynurenic acid, an antagonist of excitatory amino acid receptors. Because of the possible role of kynurenic acid in basal ganglia diseases, the distribution of kynurenine aminotransferase immunoreactivity was examined in the adult rat striatum at the light and electron microscopic levels. Kynurenine aminotransferase immunoreactivity was detected in glial cells and in neurons. The preadsorption control vastly reduced or eliminated specific staining at both the light and electron microscopic levels. Kynurenine aminotransferase positive glial cells were abundant and contained a robust and homogeneous distribution of reaction product in both the nucleus and cytoplasm. The majority of neurons, both medium and large, were immunostained and exhibited granular kynurenine aminotransferase immunoreactivity in the cytoplasm of somata and proximal dendrites. At the ultrastructural level, kynurenine aminotransferase immunoreactive astrocytic processes were apparent throughout the neuropil where they often encircled capillaries and surrounded axospinous synapses. Reaction product was associated with the cytoplasmic matrix, filaments, rough endoplasmic reticulum, and the nucleus. In neurons, the majority of label occurred in round membrane-bound cytoplasmic organelles located adjacent to the Golgi apparatus, rough endoplasmic reticulum, and the cell or nuclear membranes. Cisternae and vesicles were identifiable in some of the labeled profiles. Polyribosomes and rough endoplasmic reticulum were also labeled. These data provide an anatomical basis for biochemical studies that have suggested the presence of striatal kynurenine aminotransferase in both astrocytes and neurons.

Animals↗
PubMed1992

Effect of stereotactic thalamic lesion on essential tremor.

The cause of essential (low-frequency) tremor is unknown and its relation to physiological (high-frequency) tremor is unclear. We assessed essential tremor in one patient before and after a stereotactic thalamic lesion. The procedure changed the size of the tremor in the right hand but not in the left. Persistence of a low-frequency component suggested that essential tremor was an additional feature superimposed on physiological tremor in this patient. The focus of essential tremor seems to be an autonomous central generator that is independent of physiological tremor mechanisms.

Adult↗
PubMed1992

Methionine oxidation and inactivation of alpha 1-proteinase inhibitor by Cu2+ and glucose.

The effect of glucose/Cu2+ incubation on (a) pure methionine oxidation, (b) the oxidation of active-site methionine in alpha 1-proteinase inhibitor (alpha 1PI) and (c) the resulting activity and structural changes of this inhibitor was investigated. While no methionine was oxidized during a 24 day, 37 degrees C incubation with 0.01 M EDTA and 100 mM glucose, 64.2% oxidation occurred in 6 days when 0.01 mM Cu2+ was added to the 100 mM glucose. The first-order rate constant for oxidation in 10 mM glucose, 0.01 mM Cu2+ was 0.0218 day-1. Oxidation was inhibited by catalase, but accelerated by ascorbate ion. The active-site methionyl residue of alpha 1PI was oxidized 71.3% after a 4 day incubation in 100 mM glucose, 0.01 mM Cu2+ (pH 7.45), 0.1 M phosphate buffer. The elastase and trypsin inhibiting activities were lowered to 3.1 and 1.5% of control samples during this incubation. The inclusion of 1 mM DETAPAC, a transition metal chelator, resulted in a 98 + % retention of activity. Intrinsic fluorescence (350 nm excitation, 415 nm emission) of alpha 1PI increased 576% over control for the sample incubated in 100 mM glucose, 0.01 mM Cu2+ and SDS-PAGE revealed protein fragment molecular weights of 44.4 and 39.8 kDa. These studies suggest that both methionine oxidation and free radical induced fragmentation contribute to loss of alpha 1PI activity during glucose/Cu2+ incubations.

Binding Sites↗
PubMed1992

Relationship of thrombohemorrhagic complications to endothelial cell function in patients with chronic myeloproliferative disorders.

Thrombotic and hemorrhagic disorders are common complications of the myeloproliferative disorders. Endothelial cells release both procoagulant and profibrinolytic factors, which may contribute to these hemorrhagic or thrombotic complications. The pre- and postvenous stasis levels of the procoagulant and profibrinolytic factors produced by endothelial cells were correlated with the occurrence of complications in polycythemia rubra vera (PRV) patients (n = 29) and essential thrombocythemia (ET) patients (n = 17) compared with normal patients (n = 17). Tissue plasminogen activator (tPA) activity, plasminogen activator inhibitor (PAI) activity, von Willebrand's factor (vWF) activity and antigen (vWF:Ag), and factor VIII activity were measured. The resting tPA activity was significantly higher in the two disease groups compared with normal controls, but no difference between the levels of tPA and either complication within the disease groups was observed. Significantly elevated tPA following venous stasis was observed in the patients of both disease groups who had bleeding complications. Significant decreases, compared with the normal group, in both resting and postvenous stasis levels of PAI were observed in the disease groups regardless of complication history. The subjects from both disease groups with thrombotic complications had significantly elevated resting vWF and both resting and postvenous stasis vWF:Ag levels compared with normal controls. The endothelial cell is likely to be responding to abnormal hemostasis rather than being primarily involved in the genesis of a hyper- or hypocoaguable state.

Adult↗
PubMed1992

Transcription and autoregulation of the stabilizing functions of broad-host-range plasmid RK2 in Escherichia coli, Agrobacterium tumefaciens and Pseudomonas aeruginosa.

The broad-host-range plasmid RK2 has been shown to encode several proteins important for its maintenance within bacterial populations of a number of Gram-negative bacteria. Their genes are organized into two operons: parCBA and parD. These operons have been proposed to be transcribed from two divergent promoters, p-parCBA and p-parD, located within a sequence of approximately 150 bases. In this report we identify and characterize the sequences required for regulated transcription from these promoters in Escherichia coli, Agrobacterium tumefaciens and Pseudomonas aeruginosa. Both of these promoters are repressed by their own gene products in the same manner in all three bacteria tested, with ParA functioning as the primary repressor of p-parCBA and ParD functioning as the repressor of p-parD. The binding regions of these proteins were determined through deletion analyses, DNA mobility shift assays, and an examination of the effect of mutations in this region. Based on these observations, the ParA protein appears to bind to either two inverted repeat or two direct repeat sequences, one downstream from the transcriptional initiation site and the other upstream of the p-parCBA -35 box. The ParD protein appears to bind to one inverted repeat sequence, located between the -35 and -10 boxes of p-parD.

Agrobacterium tumefaciens↗
PubMed1992

The effects of scopolamine on event-related potentials in a continuous recognition memory task.

Event-related potentials (ERPs) were recorded during a task requiring continuous recognition memory for visually-presented words. Twelve subjects each performed the task twice, once following the administration of scopolamine, and once after receiving a saline placebo. In the placebo condition, correctly detected "old" words (i.e., words that had been presented once before during the task) evoked more positive-going ERPs than did "new" words. Scopolamine caused a substantial impairment in task performance, but did not reduce the size of these old-word/new-word ERP differences. It is concluded that old/new ERP effects are unlikely to reflect cholinergically-mediated neural activity underlying normal recognition memory.

Adult↗
PubMed1992

A region of the broad-host-range plasmid RK2 causes stable in planta inheritance of plasmids in Rhizobium meliloti cells isolated from alfalfa root nodules.

We demonstrate for the first time that the broad-host-range stabilization loci from plasmid RK2 cause total retention of plasmids in cells of Rhizobium meliloti during symbiosis with alfalfa. Two derivatives of plasmid RK2, pRK290 and a 7.3-kb mini-RK2 plasmid, were stabilized in R. meliloti cells isolated from root nodules by the insertion of a 3.2-kb DNA fragment or a smaller 0.8-kb DNA fragment derived from the RK2 stabilization region.

Aerobiosis↗
PubMed1992

Definition of a minimal plasmid stabilization system from the broad-host-range plasmid RK2.

The stable inheritance of the broad-host-range plasmid RK2 is due at least in part to functions within a region located at coordinates 32.8 to 35.9 kb, termed the RK2 par locus. This locus encodes four previously identified genes in two operons (parCBA and parD; M. Gerlitz, O. Hrabak, and H. Schwab, J. Bacteriol. 172:6194-6203, 1990, and R. C. Roberts, R. Burioni, and D. R. Helinski, J. Bacteriol. 172:6204-6216, 1990). The parCBA operon is functional in resolving plasmid multimers to monomers. Analysis of the plasmid stabilization capacity of deletions within this region, however, indicates that this multimer resolution operon is required for stabilization only in certain Escherichia coli strains and under specific growth conditions. The deletion analysis further allowed a redefinition of the minimal functional region as 790 bp in length, consisting of the parD gene (243 bp) and its promoter as well as sequences downstream of parD. This minimal region stabilizes an RK2-derived minireplicon in several different gram-negative bacteria and, at least in E. coli, in a vector-independent manner. By insertional mutagenesis, both the parD gene and downstream (3') regions were found to be required for plasmid stabilization. The downstream DNA sequence contained an open reading frame which was subsequently shown by transcriptional and translational fusions to encode a protein with a predicted size of 11,698 Da, designated ParE. Since the parDE operon requires the presence of the parCBA operon for efficient stabilization under certain growth conditions, the potential role of multimer resolution in plasmid stabilization was tested by substituting the ColE1 cer site for the parCBA operon. While the cer site did function to resolve plasmid multimers, it was not sufficient to restore stabilization activity to the parDE operon under growth conditions that require the parCBA operon for plasmid stability. This suggests that plasmid stabilization by the RK2 par locus relies on a complex mechanism, representing a multifaceted stabilization system of which multimer resolution is a conditionally dispensable component, and that the function(s) encoded by the parDE operon is essential.

Amino Acid Sequence↗
PubMed1992

Phosphorylation of the rodent negative acute-phase protein alpha 1-inhibitor-III by the insulin receptor tyrosine kinase.

alpha 1-Inhibitor-III (alpha 1I3), a broad range proteinase inhibitor, member of the alpha-macroglobulin family, is abundant in normal rat plasma. Insulin-dependent tyrosine phosphorylation of a monomeric 195K glycoprotein (pp195) was observed in wheatgerm agglutinin (WGA)-Sepharose-purified insulin receptor preparations from rat liver and muscle. Phosphorylation of pp195 in vitro required a basic poly-amino acid, i.e. poly-L-lysine. We present evidence identifying pp195 as alpha 1I3. In situ perfusion with saline essentially removed pp195 from rat livers. Addition of normal rat plasma to liver homogenates or to WGA eluates restored insulin-stimulated phosphorylation of pp195; plasma from streptozotocin-diabetic rats was much less effective. Liver-derived pp195 copurified with an abundant plasma protein, with the characteristics of alpha 1I3, on size exclusion and ion-exchange chromatography. An approximately 195K protein, comigrating with alpha 1I3, was markedly diminished in plasma from diabetic rats, and alpha 1I3 concentration was decreased by approximately 70% upon immunoblot analysis. Highly purified alpha 1I3 was phosphorylated by muscle- or liver-derived insulin receptors in the presence of 1 microM poly-L-lysine and comigrated with pp195 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. alpha 1I3 phosphorylation was half-maximal at approximately 70 nM and was stimulated by insulin 7-fold. Hindlimb perfusion removed more than 90% plasma albumin but only approximately 20% pp195 from muscles. alpha 1I3 messenger RNA was identified in liver but not in muscle. A specific antibody against alpha 1I3 immunoprecipitated phosphorylated pp195 in WGA-purified insulin receptor preparations from nonperfused liver and from saline perfused and nonperfused muscle. alpha 1I3 is bound and internalized by alpha-macroglobulin receptors; whether it is phosphorylated in vivo is unknown. Hepatic alpha 1I3 synthesis may diminish in diabetic rats.

Acute-Phase Proteins↗
PubMed1991

Event-related potentials related to recognition memory. Effects of unilateral temporal lobectomy and temporal lobe epilepsy.

Event-related potentials (ERPs) were recorded during a continuous recognition memory task for visually presented words, with a 6 item lag between the first and second presentation of each word. The subjects consisted of: (i) a control group of patients with primary generalized epilepsy; (ii) patients who had undergone either a left or a right anterior temporal lobectomy; (iii) unoperated patients with either left or right unilateral temporal lobe epilepsy. In the controls, ERPs to detected 'old' words were reliably more positive-going in the interval 300 to 600 ms post-stimulus than were ERPs to 'new' items. In both left and right lobectomy patients, 'old/new' ERP differences in the same latency range were significantly smaller than in the controls, and did not differ significantly from zero. At midline electrodes, old/new effects in the temporal lobe epilepsy patients were of similar magnitude to those of the controls. In contrast to the control data, the old/new effects in the temporal lobe epilepsy patients were asymmetric, in that they were smaller over the hemisphere ipsilateral to the seizure focus than over the contralateral hemisphere. No relationship was found across subjects between the magnitude of old/new ERP effects and verbal memory performance. In a second task, occasional non-words had to be discriminated against a background of sequentially presented words, some of which were repetitions of the immediately preceding item. ERPs evoked by repeated words were more positive-going than were those to first presentations; this effect was reliable, and of equivalent size, in all patient groups. It is concluded that in the recognition task, old/new ERP effects are dependent on temporal lobe functioning, but that the anterior temporal lobe is not the principal locus of the generators of these effects. The cognitive processes reflected by these effects do not appear to be strongly lateralized to one hemisphere, and neither do they seem to be necessary for normal verbal memory.

Adolescent↗
PubMed1991

Normal P300 following extensive damage to the left medial temporal lobe.

Event-related potentials (ERPs) were recorded during auditory and visual "oddball" tasks from a patient with a severe verbal memory deficit due to a low grade infiltrating glioma which involved the full extent of the left medial temporal lobe. In both sensory modalities, the patient's oddball-evoked P300s were symmetrical and of normal amplitude. These findings are difficult to reconcile with the hypothesis that the hippocampus, or any other medial temporal structure, makes a substantial contribution to the scalp P300.

Adult↗
PubMed1990

Immunoreactive GAP-43 in the neuropil of adult rat neostriatum: localization in unmyelinated fibers, axon terminals, and dendritic spines.

GAP-43 is a neuron-specific phosphoprotein that has been implicated in neuronal development, axonal regeneration, and synaptic plasticity. Although in mammals the caudate-putamen is among those brain areas that retain a high content of GAP-43 throughout life, the role of the phosphoprotein in the neostriatum is unknown. In order to understand better the possible function(s) of GAP-43 in the adult striatum, its cellular localization was examined with immunohistochemistry at the light and electron microscopic levels by using a sheep polyclonal antibody. At the light microscopic level immunoreactive GAP-43 was abundant throughout the neostriatal neuropil but was absent from neuronal somata. At the ultrastructural level, labeling was most prevalent in small unmyelinated axons (0.12-0.15 microns diameter). Reaction product was distributed along fibers in discrete patches about 1 micron apart and in preterminal sites from which vesicle-filled boutons arose. Staining was also present in small (0.35 microns) axon terminals that contained round vesicles and formed asymmetric synapses, mostly with thin spines. Following unilateral cortical lesions, some degenerating cortical axons in the neostriatum exhibited GAP-43 labeling. Unexpectedly, in normal striatum, GAP-43 was also occasionally found in the heads of dendritic protrusions and in thin spines that received asymmetric contacts. We speculate that in the adult neostriatum, the protein may be important in the remodeling of synapses onto medium spiny neurons that involve, in part, the corticostriatal pathway.

Animals↗
PubMed1990

Long-term survival of GABA-, enkephalin-, NADPH-diaphorase- and calbindin-d28k-containing neurons in fetal striatal grafts.

Neurons in long-term striatal grafts were examined to determine if they retain the neurotransmitter characteristics of cells in younger grafts. In addition, calbindin-d28k, a ubiquitous marker of medium spiny neurons, was used to examine the overall frequency and ultrastructural characteristics of spiny neurons in the older grafts. Grafts from 17-day fetal striata were injected into the quinolinic acid-lesioned caudate nucleus in 5 adult rats. After 16 months, the neostriatum was processed for the localization of immunoreactive GABA, calbindin, enkephalin and NADPH-diaphorase (-d) activity. The proportions of GABA-, enkephalin- and NADPH-d-labeled neurons to total Nissl-stained neurons in the 16-month-old grafts (25 +/- 6, 13 +/- 4, and 3 +/- 3, respectively) were similar to findings in 2-month-old grafts. Calbindin-positive cells formed the highest proportion (36.3 +/- 3) of labeled neurons in the older grafts. Nuclear and spine morphology of immunoreactive calbindin cells varied more in the grafts than in host caudate. Results show that there is long-term survival and stability of GABA, enkephalin and NADPH-d cell populations in the grafts and that some grafted spiny neurons may exhibit altered phenotype from those of host striatum.

Animals↗
PubMed1990

GABAergic synapses in the brain identified with antisera to GABA and its synthesizing enzyme, glutamate decarboxylase.

GABA is a known inhibitory neurotransmitter in the mammalian brain. The site of GABAergic synapses can be determined with immunocytochemical methods that localize either GABA or its synthesizing enzyme, glutamate decarboxylase (GAD). In general, GABAergic axon terminals contain pleomorphic synaptic vesicles and form symmetric synapses. However, a small number of GABAergic axon terminals in selected brain regions (spinal cord, cerebellum, superior colliculus, striatum, globus pallidus, inferior olive, and substantia nigra) form asymmetric synapses. GAD- and GABA-immunoreactive processes that contain synaptic vesicles participate in every known morphological type of chemical synapse. These include axosomatic, axodendritic, axospinous, initial segment, axoaxonic, dendrodendritic, serial, reciprocal, and ribbon synapses. Although GABAergic synapses form a heterogeneous group, they most commonly form axosomatic, axodendritic, and initial segment synapses in the brain and spinal cord. These findings provide helpful guidelines for the identification of GABAergic synapses in future studies.

Animals↗
PubMed1990

Endogenous event-related potentials from sphenoidal electrodes.

Event-related potentials (ERPs) were recorded from left and right sphenoidal electrodes during 2 cognitive tasks (visual oddball and a word repetition procedure) known to evoke endogenous ERP activity in the medial temporal lobe. Both tasks gave rise to large, reliable modulations of scalp-recorded ERPs. In the oddball task, no consistent task-related ERP activity could be recorded from the sphenoidal electrodes concurrently with the scalp-recorded P3 component, although in the latency region following the peak of P3 these electrodes exhibited an enhanced late negative wave to target stimuli. In the word repetition task, no consistent repetition-related ERP effects of any kind were observed from the sphenoidal electrodes. Sphenoidal electrodes do not appear to detect the endogenous ERP components that are generated in the medial temporal lobe concurrently with scalp-recorded components.

Acoustic Stimulation↗
PubMed1990

Evidence for synaptic proliferation, reorganization, and growth in the excitotoxic lesioned adult rat caudate nucleus.

Functional recovery following brain injury depends, in part, on the reestablishment of synaptic connections by surviving neurons. In this study we used quantitative methods to examine the synaptic organization of the caudate neuropil at 2, 7, and 30 weeks following excitotoxic injury. Results showed that in regions of severe to moderate neuronal depletion caused by intrastriatal injections of quinolinic acid, synaptic density was significantly reduced relative to controls but was significantly greater than neuronal density (percentage of control) at all postlesion intervals. Moreover, there was a marked increase in synaptic density (percentage of control), but not neuronal density (percentage of control), in the lesion periphery between 7 and 30 weeks postlesion. The relative proportion of axospinous synapses to total synapses was significantly reduced in the center of the lesion at all postlesion intervals but was similar to controls in regions of neuropil that were less severely affected. In the lesion and its borders there was also a significant increase in the proportion of short synaptic contacts between axons and spines and a proliferation of small unmyelinated fibers. Furthermore, after 30 weeks postlesion, regions of severe neuronal depletion developed aberrant synaptic contacts between vesicle-containing profiles which were significantly larger than those in normal caudate. We conclude that excitotoxic lesions of the neostriatum precipitate a variety of responses in injured neuropil including synaptic proliferation, growth, and altered circuitry.

Animals↗